JPS61260108A - Three-dimensional measuring method - Google Patents

Abstract

PURPOSE:To obtain a method capable of easy automatic measurement and having high contrast by scanning an object to be measured with the aid of a sine wave mode intensity modulated light beam having a constant modulation frequency and creating a striped pattern on the object. CONSTITUTION:The light oscillated from a semiconductor laser 1 scans the object 6 through the hologram lens 5 of a holographic laser scanner 4. At this time an encoder 12 fetches the rotational frequency signal of the scanner into an arithmetic controller 11. Receiving an encoder output synchronizing signal, the controller 11 transmits a control signal so as to output the sine wave having the decided frequency to a waveform forming device 10. After the output signal of the device 10 is converted into a sufficient current to drive the laser 1 by an amplifier 9, the laser 1 is modulated to a sine wave. Then a television camera 7 picks up the image of a sine wave-like fringe deformed on the surface of the object. The striped pattern corresponding to a signal generated by the device 10 is previously inputted to an image processor 8, is overlapped with the image picked up by the camera 7, thereby creating a moire fringe.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to three-dimensional measurement using stripes, particularly as typified by moire topography.

(Prior art and its problems) Moiré topography projects a striped pattern onto a physical surface, superimposes the striped pattern deformed by the shape of the object and the standard striped pattern, and analyzes the moiré fringes that occur as the difference frequency. This is a method of measuring the shape of an object. For more information, see the magazine ``Applied Optics J (
Applied 0ptics).

9, 1970, pages 1467-1472, the paper “Moir! Top
stated in the month of ography. In this method, a point light source 21 illuminates a grating 22 placed directly in front of an object 23 as shown in FIG.

There are a grating irradiation type and a grating projection type in which an image of a grating 24 installed in an optical system is formed on the object plane as shown in FIG. When comparing both methods, the latter is more flexible and has a wider range of applications in terms of operability. Regarding grid projection type moiré topography, for example, see the magazine "Applied Optics, Vol. 22,
1983, paper on pages 850-855 [
Projection Moire using moving grid method in automatic 3D topography (Projection Mo1r6 wi
th moving grants for an
tomated 3-D topography) J
is described in detail. In general, moire measurement produces high-order moire fringes, so when automatically analyzing the fringes, it is difficult to separate them from desired moire fringes. In order to remove these high-order moiré fringes, a moving grid method was developed that averages out the high-order moiré fringes by moving the grating during observation.

For details, see the above magazine (Applied Optics), Volume J9, 19.
1467-1472, the paper “Moir6Topography”
It is stated in J.

(Problems to be Solved by the Invention) The conventional moving grating method requires mechanical movement to move the grating, making automatic measurement difficult. The disadvantage was that the contrast was low.

(Objective of the Invention) The object of the present invention is to provide a three-dimensional measurement method that eliminates high-order moiré fringes without moving the grating, facilitates automatic measurement, and obtains desired moiré fringes with high contrast. It's about doing.

(Means for solving the problem) This invention scans an object to be measured with sinusoidal intensity modulated light having a constant modulation frequency, generates a striped pattern on the object surface, and deforms it depending on the shape of the object. This three-dimensional measurement method is characterized in that the striped pattern is superimposed on a reference striped pattern in the form of a sine wave having the same frequency as the intensity modulated light.

(Operation/Principle) In a holographic laser beam scanning device such as a holographic laser scanner, several holograms are arranged and fixed on the circumference of a disk, and the laser beam is scanned by rotating the holograms at high speed. If the front optical system of a holographic laser scanner is adjusted so that the scanning beam converges in the scanning direction on the object plane and diverges in the sub-scanning direction, the beam width in the sub-scanning direction
The length determined as the scan length is scanned over the entire surface. At this time,
By modulating the laser, a striped pattern can be created in the scanning direction. Consider a conventionally used rectangular grid with amplitude transmittance of 0 or 1. , define a periodic function f(x) as follows.

Below, the formula (1) is expanded into a Fourier series. According to equation (2), the amplitude transmission function of a simple rectangular grid with a black-to-white ratio of 1:1 is. In equation (3), P and ■ represent spatial frequencies in the X direction and the X direction, respectively. When formula (3) is Fourier transformed, Xtxp (CxE, +y11)) dxdy = L meeting δ (+
y)”A(δ(X-λfp, y-λfv) ten δ(2+λ
h, y + λf
v)+8cx+3λ/)1.31 +3λ/Y))n...+n2...(4). However, λ represents the wavelength, and f represents the focal length of the Fourier transform lens. The second term in equation (4) represents ±1-order moire fringes, and the third and subsequent terms represent unnecessary higher-order moire fringes.

On the other hand, the amplitude transmission function of a sinusoidal simple grating is.

When formula (5) is Fourier transformed, it can be seen that formula (6) does not produce higher-order moiré fringes compared to formula (4). The above discussion also holds true for general grids. Therefore, by modulating the laser into a sinusoidal waveform and projecting it onto the object, measurement without high-order moiré fringes can be achieved.

(Example) FIG. 1 shows an example in which the method of the present invention is applied to moiré topography configured by a semiconductor laser 1 and a holographic laser scanner 4. The light emitted from the semiconductor laser 1 is collimated by a collimating lens 2, converted into an elliptical beam by a cylindrical lens 3, and then sent to a holographic laser scanner 4.
An object 6 is scanned by a hologram lens 5. At this time, as shown in the timing chart shown in FIG. 2, the encoder 12 converts the rotation period signal (a) of the scanner into
It is incorporated into an arithmetic and control device 11 such as a microcomputer having a P-IB interface. The arithmetic and control device 11 receives the encoder output synchronization signal (a) and outputs a sine wave (e) of a predetermined frequency to a waveform forming device 10 such as a function generator having a GP-IB interface. A control signal (b) is sent to. The determined frequency is (n+w)/60 Hz, where Wrpm is the rotational speed of the scanner, n is the number of lenses arranged in the scanner, and t is the number of stripes to be scanned on the object plane. The output signal (C) of the waveform forming device 10 is made into a current (d) sufficient to drive the semiconductor laser 1 by the amplifier 9, and then modulates the laser into a sinusoidal waveform. An example of the output of the waveform forming device is shown in FIG. The TV right camera, which can accumulate light, images the sinusoidal stripes deformed on the object plane. A multi-gradation image processing device 8, which has multiple frame memories and a GP-IB unsintered face, and has inter-image integration, addition and subtraction functions, calculates and controls the striped pattern corresponding to the signal generated in advance by the waveform forming device 10. Input from device 11, and then
Moiré fringes are generated by superimposing the image with the image captured by the camera 7. FIG. 4 shows an example of a striped pattern that is input in advance to the image processing device 8. The four arithmetic operations for images are to digitally represent the gradation of an image and perform gradation calculations for each dot. Since there are intermediate tones in the stripes, there are also intermediate tones in the moiré fringes, and an image processing device that can perform multi-gradation calculations is required. This image processing device performs the calculations described in the section on operation and principle to generate moiré fringes.

(Effects of the Invention) As detailed above, according to the three-dimensional measurement method of the present invention, high-contrast images can be obtained as high-order moire fringes without moving the grating, unlike the conventional grating movement method. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a timing chart of system signals, FIG. 3 is a diagram showing a current waveform injected into a semiconductor laser in the embodiment, and FIG. In the example, FIG. 5 is a diagram showing an example of the density distribution of the reference stripes stored in the image processing device, FIG. 5 is a diagram showing a conventional example of grating irradiation type moire topography, and FIG. 6 is a diagram showing a conventional example of grating projection type moire topography. FIG. In the figure, 1... Semiconductor laser 2... Collimating lens 3... Cylindrical lens 4... Holographic laser scanner 5... Hologram lens 6... Object 7... TV right camera
8... Image processing device 9... Amplifier
10... Waveform forming device 11... Arithmetic control device
12...Encoder 21...Light source 2
2... Lattice 23... Object 24...
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Claims (1)

[Claims] A striped pattern is generated on the object surface by scanning the object to be measured with a sinusoidal intensity modulated light having a constant modulation frequency, and a striped pattern deformed depending on the shape of the object and a sine wave having the same frequency as the intensity modulated light are generated. A three-dimensional measurement method characterized by overlapping a wavy reference striped pattern.